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1. Change the #4 spark plug.
2. Do you best to take a look at the #4 cylinder if you have a borescope. Do this with the spark plug still installed. Sometimes you spot the problem just by looking at it. I had a very similar problem as you did, turned out to be water in the No6 spark plug chamber.

Its a 6 cylinder. Coil's not that expensive but its not that cheap and is hardly the problem. I knew someone who had a persistent cold start problem, which was ultimately traced to morning condensation seeping through his coil wires. Problem was fixed by changing it.

Dude, i had another listen to your video. I think your spark plugs may be loose. Tighten each one again, and once again, check to see if there's water in the spark plug tube. At may be lose if they were not properly tightened when you changed them.

Another tip...spray wd40 into the ends of the ignition leads and try to slosh it about abit before draining the fluid. Leave them hanging loose for 10 minutes before plugging them back in.